Since the beginning of oil production from subsurface formations, the industry has been concerned with efficient control of the movement of unconsolidated formation particles, such as sand, into the wellbore. For example, such particle movement commonly occurs during production from completions in loose sandstone or following hydraulic fracture of a formation. Production of these materials causes numerous problems in the operation of oil, gas or water wells. These problems include plugging of formations, tubing and subsurface flow lines, as well as erosion of tubing, downhole equipment and surface equipment. These problems lead to high maintenance costs and unacceptable well downtime. Accordingly, numerous methods have been utilized to control the movement of unconsolidated particles during the production of fluids.
Gravel packing is one of the most common methods to prevent the production of sand. Generally, gravel packing involves placing pack sand, an aggregate of particulate material, in the annular space between the wellbore and a fluid permeable, perforated base pipe that is located adjacent to the production zone. A particular pack sand is selected to prevent the flow of formation particles therethrough, taking into consideration the characteristics of the particular reservoir. The perforated base pipe is designed to allow production fluids to flow therethrough with minimum resistance, while preventing both the pack sand and the formation particles from flowing into the production string. Gravel packing is commonly achieved by either an open hole gravel packing procedure or an internal gravel packing procedure, depending on the characteristics of the particular reservoir.
In addition to the use of a perforated base pipe and gravel packing, a sand control screen is commonly employed to control the movement of formation particles. These screens may comprise a continuous single wire wrapped around the base pipe. While this type of screen is capable of excluding even the smallest API grades of pack sand, these screens are easily damaged during handling, installation and production.
More recently, a sand control screen comprising a sand control screen jacket has been used. The screen jacket is fully formed from a single wire prior to attachment to the base pipe. Commonly, a plurality of ribs extend longitudinally along the internal surface of the screen jacket to provide strength to the wire and a stand-off between the wire and the base pipe once the screen jacket is attached. In addition, some screen designs use prepacked sand confined around the perforated base pipe. These prepacked screens are constructed by fabricating the metal components, then forcing pack sand, either resin coated or uncoated, between the perforated base pipe and an inner wire screen or between an inner wire screen and an outer wire screen of a multi-layer screen.
In the past, various U.S. patents have issued relating to such filter screens. For example, U.S. Pat. No. 3,958,634, issued on May 25, 1976 to H. F. Smith III, describes a welded wire well screen on a perforated casing. The wire screen sleeve has longitudinal wires arranged in a generally cylindrical shape. An external wrapping wire is welded thereto. This screen is positioned over a perforated pipe having an external diameter substantially equal to the internal diameter of the sleeve. Annular welds are provided between each end of the wire screen and the pipe so as to close the space therebetween and to secure the sleeve to the pipe.
U.S. Pat. No. 4,260,016, issued on Apr. 7, 1981 to R. Calderon, describes a self-cleaning helical spring sand screen. This sand screen includes a hydraulically-actuated spring-based spool valve connected to the upper end of the sand screen for receiving liquid under high pressure, for storing energy in the spring, for expanding the helical spring sand screen, and for ejecting liquid into the helical spring sand screen for cleaning thereof.
U.S. Pat. No. 4,293,037, issued on Oct. 6, 1981 to R. Calderon, describes a method of forming and assembling the self-cleaning helical spring screen of the type disclosed in U.S. Pat. No. 4,260,016.
U.S. Pat. No. 4,494,603, issued on Jan. 22, 1985 to J. E. Harguindey, describes an improved wire mesh well screen which is defined by a helically-wrapped strip of wire mesh which is supported by a rigid cage-like structure of welded steel longitudinal support rod and helical wrap wires. The wire mesh strip is helically wound with a gap and at least one wrap wire is helically wound in the gap so that a small portion of its width can be firmly adhered to the rods while at least another portion of its width overlies an adjacent side edge of the mesh strip.
U.S. Pat. No. 5,411,084, issued on May 2, 1995 to J. B. Padden, teaches a sand filter system for use in a well. A tubular wedge wire screen is telescopically positioned on the tubing covering the perforations. A plurality of tubular corrugated filter elements are then positioned on the wedge wire screen in an end-to-end relationship. Each of the filter elements is formed of diffusion bonded multiple layers of wire mesh and each of the filter elements is corrugated to provide an external surface having an area at least three times the area of the cylindrical external surface of the tubular wedge wire screen that is encompassed by each filter element.
U.S. Pat. No. 5,787,980, issued on Aug. 4, 1998 to Sparlin et al., describes a well screen having a uniform diameter. Each of the screen units has a cylindrical connecting section at least at one end thereof and includes a plurality of support rods extending in the axial direction of the screen and disposed cylindrically about a section of the screen other than the connecting section at a predetermined interval in the circumferential direction of the screen. A wire is wound on the outer periphery of the support rod so as to form slits of a predetermined width.
U.S. Pat. No. 5,938,925, issued Aug. 17, 1999, to Hamid et al., teaches a progressive gap sand control screen having a plurality of parallel ribs spaced about an axis and a screen wire wrapped around the plurality of ribs having turns which extend along the length of the plurality of ribs such that adjacent turns have gaps therebetween. The gaps form a gap profile in which the gaps near the upper end of the sand control screen are narrower than the gaps near the lower end of the sand control screen. The width of the gaps near the upper end of the sand control screen are less than the diameter of the particles which cause erosion. The gap profile includes a variable gap section near the upper end of the sand control screen and a constant gap section below the variable gap section.
U.S. Pat. No. 6,298,914, issued on Aug. 9, 2001 to Spray et al., describes a wire-wrapped well screen for placement within wells and used to filter out impurities from the fluid entering the well. The well screen includes a spirally-wound wire forming a cylinder with gaps between the layers of the wire. The layers of the wire are attached by spacers placed within the gaps.
FIG. 1 is an illustration of a prior art technique for forming such wire wound filter screens. The process 1 of the prior art includes placing a plurality of ribs 2 into a carrier mechanism 3 which has an axis of rotation 4. Ribs 2 are spaced around and oriented around axis 4 to form a generally cylindrical shell for the screen 5. Carrier mechanism 3 is rotated about the axis of rotation 4 and laterally advanced while the screen wire 6 is wrapped around the ribs 2 forming adjacent turns which have gaps therebetween such as turns 7, 8 and 9. The screen wire 6 is also known as “wrap wire”. The screen wire 6 is adhered to each of the ribs 2 by welding mechanism 10.
The gap profile of screen 5 is a function of the linear velocity and the angular velocity of the carrier mechanism 3. By varying either the linear velocity or the angular velocity of carrier mechanism 3, the desired gap profile may be obtained. For example, the gap profile in which the gaps is near the upper end of the screen 5 are narrower than the gaps near the lower end of the screen 5 may be achieved by increasing the linear velocity of carrier mechanism 3 while maintaining a constant angular velocity or decreasing the angular velocity of carrier mechanism 3 while maintaining a constant linear velocity as the carrier mechanism 3 laterally advances.
Unfortunately, it has been found that one of the failures of the technique shown in FIG. 1 is the inability to accurately account for variation in wire diameter. Wire manufacturing processes are such that the wire may tend to increase or decrease in diameter during the manufacturing processes. As such, with the technique shown in FIG. 1, if relatively wide diameter wire is wound next to relatively wide diameter wire, the gap will be too small to be effective. On the other hand, if the wire diameter is narrow, then the gap between adjacent surfaces of the wrap wire 6 will be too large and would allow sand intrusion. As such, a need has developed to be able to control the wrapping of the wire screen 5 while controlling the gap space between the adjacent surfaces of wire. This is necessary to overcome the inability of wire manufacturers to accurately control the wire diameter over long lengths of production.
It is an object of the present invention to provide an apparatus and method for manufacturing wire wound filter screens.
It is another object of the present invention to provide an apparatus and method whereby the gaps between adjacent surfaces of the wrap wire are accurately controlled.
It is a further object of the present invention to provide an apparatus and method for manufacturing wire wound filter screens in which a rolling electrode constantly contacts the surface of the wrap wire during the production of the filter screen.
It is further object of the present invention to provide an apparatus and method for manufacturing wire wound filter screens which effectively prevents arcing of the electrode during the welding process and also avoids the pitting of the wire by virtue of the arcing.
It is further object of the present invention to provide an apparatus and method for manufacturing wire wound filter screens which effectively controls the translation of the rib wires relative to the size of gaps that are produced between adjacent surfaces of wrap wire.
It is another object of the present invention to provide an apparatus and method for manufacturing wire wound filter screens which is easy to use and relatively inexpensive.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.